1. Field of the Invention
This invention relates to a hydraulic pig advance system comprising a control volume chamber containing hydraulic fluid and a force transmitting member. The system further comprises two directional control valves which can be selectively repositioned to cause hydraulic fluid to cycle the force transmitting member back and force such that in each cycle, a metered amount of hydraulic is transmitted into a pig housing where it causes a pig to move a predetermined distance.
2. Description of the Prior Art
Pressurized accumulators have been used to use an injection burst of pressurized fluid to advance a pig in a process fluid line. The use of only a pressurized accumulators does not provide for precise control of the distance that the pig is advanced.